Numerous techniques are known for separating thin-walled thermoformed articles from sheets of thermoformable plastic material. The trimming of thermoformed articles from a continuous web or sheet of thermoformable plastic material has long been known in the art. It has been known to form and sever articles from webs of both solid and foamed-plastic material.
Using a thermoforming process, articles are molded into a heated material web using a thermoforming machine. A heated web of material is transported through the thermoforming machine where articles are then formed in the web. The web is then transported from the thermoforming machine at a relatively high operating speed into a trim press where the articles are severed from the web of plastic material.
Typically, a trim press includes cooperating male and female members, each member having cooperating cutting surfaces, such as complementary punches and dies that correspond with an outer configuration of the formed articles. Such pairs of punches and dies are adapted to cooperate and trim individual articles from the web as they are brought together on opposite sides of the web by the trim press. Recently, attempts have been made to further increase the operating speed of trim presses. Such increases in operating speed can lead to significant increases in throughput and article output. Accordingly, relatively high-speed trim presses have been developed that generate a continuous horizontally-nested stack of articles which are slid onto a platform, or packing table. However, increases in operating speed have caused some problems in that a vacuum is created when drawing apart platens of a trim press which can actually suck severed articles or scrap web material back up into the trim press dies, which can create a jam or problem when running the trim press at relatively high operating speeds.
FIGS. 7–8 illustrate one prior art solution in the form of an article accumulator 250 that is mounted onto a trim press similar to the trim press depicted with reference to FIG. 1 wherein article ejector 250 substitutes for the new article ejector that is described with reference to FIGS. 1–6 and 9–11, as described in the Detailed Description, below. For the case of the prior art article ejector 250, a support frame 252 is secured to a top face of an upper platen (not shown), such as the upper platen depicted with reference to FIGS. 1 and 2. Support frame 252 is secured via four mounting blocks 336, 338, 340, and 342 via threaded fasteners. A pair of vertical die posts 312 and 314 are also supported within the upper platen via fastener collars 332 and 334. Die posts 312 and 314 are rigidly and vertically secured within the upper platen. An ejector bridge 310 is supported by a bushing assembly 316 and 318 at each end for vertical up and down reciprocation along die posts 312 and 314. A plurality of ejector paddle assemblies depend downwardly from ejector bridge 310, such as ejector paddle assembly 344, for ejecting articles that are severed between male and female dies of a trim press into an accumulator cavity, where the articles are stacked and accumulated for delivery to a conveyor.
According to the construction of prior art article ejector 250, a servo motor 262 drives a drive pulley 320 which further drives a driven pulley 324 via a timing belt 330. Driven pulley 324 is rigidly affixed onto a drive shaft 308 in order to drive a driven wheel 322 at its opposite end. Wheel 322 and pulley 324 each pivotally support one end of a crank arm 326 and 328, respectively. Crank arms 326 and 328 are fixed with bearings at opposite ends to mounting positions on ejector bridge 310 so as to drive ejector bridge 310 and paddle assemblies 344 up and down so as to eject and clear product from between dies of a trim press during operation.
As shown in FIG. 7, support frame 252 includes side plates 300 and 302 which are joined together via rigid cross-shafts 304 and 306.
Article ejector 250, according to prior art techniques, is run in two operating modes. First, article ejector 250 is normally run to downwardly press (or eject) severed articles from dies and into a stack within an article accumulator (not shown). During such normal operating mode, pulley 324 and wheel 322 are driven between a 12:00 o'clock and 3:00 o'clock position by driving drive pulley 320 back and forth in clockwise and counter-clockwise directions, respectively, via operation of servo 262. Accordingly, crank arms 326 and 328 are only driven to half their maximum displacement position as dictated by the attachment points in the diameters on wheel 322 and pulley 324.
Another operating mode is desired in order to eject plastic material or damaged articles when there has been a misfeed or jam in a trim press. During such an operating mode, it is desirable to more deeply and fully stroke paddle assemblies into the female bores beneath a female die to eject any waste or damaged articles or material to clean out the trim press dies and cavities. In order to achieve such a result, the prior art techniques provided by article ejector 250 require operation of servo motor 252 to drive wheel 322 and pulley 324 between the 12:00 o'clock and 6:00 o'clock positions by driving drive pulley 320 in respective clockwise and counter-clockwise directions.
Accordingly, the two operating modes require that normal operation occur between a 12:00 o'clock and 6:00 o'clock position on pulley 324 which does not provide maximum stroke for a given amount of mechanical advantage as provided by the accompanying kinematic linkages (and in the first operating mode). Secondly, the clockwise and counter-clockwise reciprocating motion of the kinematic linkages in servo motor 262 is not efficient or optimal for high-speed operation. The associated moments of inertia are undesirable for relatively high operating speeds because the associated masses of the kinematic components suddenly change (or reverse) direction at high speed, which is undesirable and creates imbalance forces and increasing loading at component connections.
Accordingly, improvements are needed to provide a more efficient and high-speed article ejector for a high-speed thermoforming trim press. Furthermore, it is desirable to provide more optimal use of kinematic linkages and to reduce the negative effects of inertial operating forces to increase the operating speed and effectiveness of an article ejector.